You might know Watling Street as a shortcut in the heart of the City of London where crumpled-looking office workers dash on their way to somewhere else or linger after work for an expensive pint. But as John Higgs explains, the street is more than a quaint rat run with a Dick Whittington vibe. While its origins are “far older than recorded history”, it remains one of the great highways of modern Britain, running virtually unbroken from Dover to Anglesey. You probably don’t recognise it because it mostly goes by other names: the A2, the A5 and, when it’s feeling fancy, the M6 Toll. Sometimes, as it wiggles its way through the market towns of central England, it becomes simply “the high street”.

Around the time of last year’s referendum, Higgs set out to explore the people and places around Watling Street. The idea was to take a series of soundings about where modern Britain (or rather, England with a top slice of Wales) sees itself today. What stories did we tell about ourselves that resulted in the vote to leave the EU? What new versions might be needed now if we are to start to resolve the bitter disagreements that the referendum laid bare?

Where the motorway crosses over the Roman road section of Watling Street, the ghosts of 20 legionaries floated into view

Higgs puts us on notice that we will need to dig deep. He recalls the moment in 2003 when a local family was travelling on the M6 in Staffordshire. Just at the point where the motorway crosses over the Roman road section of Watling Street, the ghosts of 20 legionaries floated into view. Their legs weren’t visible, which makes sense when you recall that today’s street is a whole shin-height higher than it was in the first century when the Romans tiled over ancient British trackways. Only by digging down through the intervening layers of material and psychic rubble, Hicks suggests, will we find an alternative account of where we have come from and a clue as to where we might go next.

It is concerning these moments of what Robert Macfarlane calls “English Eerie”, when an uncanny visitation from the past disrupts the placid domestic present, that Higgs is at his most persuasive. On the London leg of his journey he meets Southwark’s resident shaman, the visionary poet John Constable. Every year, Constable mounts a piece of raucous street theatre dedicated to honouring the women who worked in the medieval brothels around Southwark Cathedral, yet whose spent bodies were denied a dignified burial. In an annual act of reparation and celebration, Constable leads his motley crew – a ramshackle crowd of goth morris dancers, rough sleepers and the simply curious – to the gates of what was once Cross Bones graveyard and hollers out the names of the outcast women, one by one.

This mood of ecstatic recuperation is still going strong a hundred miles further up Watling Street where Higgs encounters Alan Moore, the revered comic book author of V for Vendetta and Watchmen. Last year Moore published Jerusalem, a novel of Blakean brightness which suggested that Northampton is the omphalos of the nation, the midpoint of England’s “dreamtime” where past, present and future come together in a subversive shiver. What thrills Higgs about Moore, Constable and other survivors of the postwar counterculture is the way that these ageing seers and sages have stayed true to their early ideals. Unconcerned about money, happy to stay in the town, even the house, in which they were born, they continue to serve a vision of the world in which spirituality and metaphysics are indivisible from progressive politics and social justice.

Just how desperately we need such a dose of utopia becomes apparent when Higgs stops off at Dunstable, which sits at the point where Watling Street crosses another ancient track, the Icknield Way. Dunstable was once a thriving market town with the usual mix of Waitrose, Sainsbury’s and local independents; now it is mostly boarded up, and the remaining chains look shifty. The reason, economists argue, is because large retailers decided to open out-of-town megastores and consumers migrated to online shopping. But for Higgs, Dunstable’s sorry state is less about the cruel logic of late capitalism and more about the town’s inability to tap into the “noosphere”, a term coined in the 1920s to describe that rich mulch of shared culture, thought, myth and law from which inspiration and rebirth spring. Heading towards the one bit of new building in the town, Higgs finds that the Grove theatre complex is already promising that this year’s pantomime, still eight months away, will star someone from Coronation Street and two contestants from Britain’s Got Talent. No wonder, he suggests, that central Bedfordshire voted overwhelmingly to leave Europe: “all you know is that it will be something different, so that’s what you choose”.

As long as Watling Street stays in the realm of the noosphere, of myth and story, then it does just fine. It’s when Higgs starts to suggest a way that this world of Miss Havisham (Rochester) and Benny Hill (St Albans), not to mention Alan Turing (Bletchley Park) and Indiana Jones (Elstree Studios, Borehamwood), might somehow translate into direct action in Brexit Britain that things start to feel implausible. A broadside against private education (Tom Brown’s Schooldays, Rugby) and the suggestion of a land value tax (Weston Park, Lichfield) stand out from a narrative that proclaims its indeterminacy. Towards the end, Higgs reveals that, over the course of his journey, he has given us three alternative explanations for how Ian Fleming (St Margaret’s Bay, Dover) came up with James Bond’s 007 handle. It could be after a Kent bus route, or a first world war German code, or the cipher used by the Elizabethan magician John Dee. The point, Higgs says, is that all of these stories have a plausible provenance and we are free to pick the one we like best. This may be a lovely advertisement for the rich plurality of the noosphere, but won’t be much help in finding a new island story on which all Britons can agree. A complacency about the corrosive power of “alternative facts” is surely what got us into this mess in the first place.

•Watling Street: Travels Through Britain and its Ever Present Past by John Higgs (W&N, £18.99). To order a copy for £16.14, go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min. p&p of £1.99.